Before we can get on with proper sciencing, we're going to need to check our equipment.
Our primary equipment are brains. We each have direct access to one, and indirect access to many more.
I don't know what brains are made out of, but they are pretty useful. They also don't behave the way you might think.
Daniel Kahneman has written an amazing book called Thinking, Fast and Slow that goes into this in detail, and really ought to be read by everyone. You can also read about cognitive biases on Wikipedia.
In a nutshell, the first and most important thing we can do to be more scientific is to distrust our brains. Our guesses are probably wrong, our memory is probably wrong, the examples that we think of are suspect, the estimates we make are overly optimistic, we value stories over data, we find it hard to process information that doesn't fit with our existing opinions, we answer the questions we find easy rather than the questions that matter.
Next time: our next-most important tool, and some ways we can use it.